Abstract
It is known that the retrieval of aerosol extinction and backscatter coefficients from lidar data acquired through so-called total-power channels – intended to measure the backscattered power irrespective of the polarization – can be adversely affected by varying depolarization effects produced by the aerosol under measurement. This effect can be particularly noticeable in advanced multiwavelength systems, where different wavelengths are separated using a system of dichroic beam splitters, because in general the reflection and transmission coefficients of the beam splitters will be different for fields with polarization parallel or perpendicular to the incidence plane. Here we propose a setup for multiwavelength aerosol lidars alleviating diattenuation effects due to changing depolarization conditions while allowing measure linear depolarization.
Highlights
Advanced aerosol-lidar systems use several transmitted wavelengths and several receiving channels, both elastic and Raman, for the rangeresolved measurement of the extinction and backscatter coefficient of atmospheric aerosols at different wavelengths
Perpendicular between themselves, ii) the backscattering medium does not change the polarized part of the returned radiation with respect to the polarization of the transmitted beams [8] [10], nor does it the part of the optical receiving system before the beam splitters, and iii) all the beam splitters in the receiver setup are arranged in such a way that the incidence plane is the same for all of them, the sensitivity of the receiver to the depolarization produced by the medium can be suppressed by orientating the incidence plane to be at a 45o angle with respect the polarization direction of the polarized part of the return radiation, irrespective of the transmission ratio
Quarter-wave plate the depolarized light is Id I I|| ), whence it can be extracted and calibrated using the setup outlined in fig. 1, where the equivalent beam splitter represents any combination of beam splitters with the sole condition that they share their incidence planes
Summary
Advanced aerosol-lidar systems use several transmitted wavelengths and several receiving channels, both elastic and Raman, for the rangeresolved measurement of the extinction and backscatter coefficient of atmospheric aerosols at different wavelengths. Perpendicular between themselves, ii) the backscattering medium does not change the polarized part of the returned radiation with respect to the polarization of the transmitted beams [8] [10], nor does it the part of the optical receiving system before the beam splitters, and iii) all the beam splitters in the receiver setup are arranged in such a way that the incidence plane is the same for all of them, the sensitivity of the receiver to the depolarization produced by the medium can be suppressed by orientating the incidence plane to be at a 45o angle with respect the polarization direction of the polarized part of the return radiation, irrespective of the transmission ratio In this case the depolarization information after transmission or reflections is found in the 3rd and 4th components of the Stokes vector, whence it can be retrieved with a quarter-wave plate and linear polarizer arrangement
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